| 143401 | December 20 | Death | 2014 – William Lowell Putnam III, American mountaineer and businessman (b. 1924) |
| 143402 | December 20 | Holiday and observance | Abolition of Slavery Day, also known as Fête des Cafres (Réunion, French Guiana) |
| 143403 | December 20 | Holiday and observance | Bo Aung Kyaw Day (Myanmar) |
| 143404 | December 20 | Holiday and observance | Christian feast day:Dominic of SilosO ClavisUrsicinus of Saint-UrsanneKatharina von Bora (Lutheran)December 20 (Eastern Orthodox liturgics) |
| 143405 | December 20 | Holiday and observance | Earliest date for Winter solstice's eve (Northern Hemisphere), and its related observances:Yaldā (Iran) |
| 143406 | December 20 | Holiday and observance | International Human Solidarity Day (International) |
| 143407 | December 20 | Holiday and observance | Macau Special Administrative Region Establishment Day (Macau) |
| 143408 | December 21 | Event | 69 – The Roman Senate declares Vespasian as Roman emperor, the last in the Year of the Four Emperors. |
| 143409 | December 21 | Event | 1124 – Pope Honorius II is elected. |
| 143410 | December 21 | Event | 1140 – Conrad III of Germany besieged Weinsberg. |
| 143411 | December 21 | Event | 1237 – The city of Ryazan is sacked by the Mongol army of Batu Khan. |
| 143412 | December 21 | Event | 1361 – The Battle of Linuesa is fought in the context of the Spanish Reconquista between the forces of the Emirate of Granada and the combined army of the Kingdom of Castile and of Jaén resulting in a Castilian victory. |
| 143413 | December 21 | Event | 1598 – Battle of Curalaba: The revolting Mapuche, led by cacique Pelentaru, inflict a major defeat on Spanish troops in southern Chile. |
| 143414 | December 21 | Event | 1620 – Plymouth Colony: William Bradford and the Mayflower Pilgrims land on what is now known as Plymouth Rock in Plymouth, Massachusetts. |
| 143415 | December 21 | Event | 1826 – American settlers in Nacogdoches, Mexican Texas, declare their independence, starting the Fredonian Rebellion. |
| 143416 | December 21 | Event | 1832 – Egyptian–Ottoman War: Egyptian forces decisively defeat Ottoman troops at the Battle of Konya. |
| 143417 | December 21 | Event | 1844 – The Rochdale Society of Equitable Pioneers commences business at its cooperative in Rochdale, England, starting the Cooperative movement. |
| 143418 | December 21 | Event | 1861 – Medal of Honor: Public Resolution 82, containing a provision for a Navy Medal of Valor, is signed into law by President Abraham Lincoln. |
| 143419 | December 21 | Event | 1872 – Challenger expedition: HMS Challenger, commanded by Captain George Nares, sails from Portsmouth, England. |
| 143420 | December 21 | Event | 1879 – World première of Henrik Ibsen's A Doll's House at the Royal Theatre in Copenhagen, Denmark. |
| 143421 | December 21 | Event | 1883 – The Royal Canadian Dragoons and The Royal Canadian Regiment, the first Permanent Force cavalry and infantry regiments of the Canadian Army, are formed: . |
| 143422 | December 21 | Event | 1907 – The Chilean Army commits a massacre of at least 2,000 striking saltpeter miners in Iquique, Chile. |
| 143423 | December 21 | Event | 1910 – An underground explosion at the Hulton Bank Colliery No. 3 Pit in Over Hulton, Westhoughton, England, kills 344 miners. |
| 143424 | December 21 | Event | 1913 – Arthur Wynne's "word-cross", the first crossword puzzle, is published in the New York World. |
| 143425 | December 21 | Event | 1919 – American anarchist Emma Goldman is deported to Russia. |
| 143426 | December 21 | Event | 1923 – United Kingdom and Nepal formally signed an agreement of friendship, called the Nepal–Britain Treaty of 1923, which superseded the Treaty of Sugauli signed in 1816. |
| 143427 | December 21 | Event | 1936 – First flight of the Junkers Ju 88 multi-role combat aircraft. |
| 143428 | December 21 | Event | 1937 – Snow White and the Seven Dwarfs, the world's first full-length animated feature, premieres at the Carthay Circle Theatre. |
| 143429 | December 21 | Event | 1941 – World War II: A formal treaty of alliance between Thailand and Japan is signed in the presence of the Emerald Buddha in Wat Phra Kaew, Thailand. |
| 143430 | December 21 | Event | 1946 – An 8.1 Mw earthquake and subsequent tsunami in Nankaidō, Japan, kills over 1,300 people and destroys over 38,000 homes. |